Browsing by Author "Donahue, Seth W., advisor"

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Open Access
Bio-inspired design for engineering applications: empirical and finite element studies of biomechanically adapted porous bone architectures
(Colorado State University. Libraries, 2020) Aguirre, Trevor Gabriel, author; Donahue, Seth W., advisor; Ma, Kaka, committee member; Heyliger, Paul, committee member; Simske, Steven, committee member
Trabecular bone is a porous, lightweight material structure found in the bones of mammals, birds, and reptiles. Trabecular bone continually remodels itself to maintain lightweight, mechanical competence, and to repair accumulated damage. The remodeling process can adjust trabecular bone architecture to meet the changing mechanical demands of a bone due to changes in physical activity such as running, walking, etc. It has previously been suggested that bone adapted to extreme mechanical environments, with unique trabecular architectures, could have implications for various bioinspired engineering applications. The present study investigated porous bone architecture for two examples of extreme mechanical loading. Dinosaurs were exceptionally large animals whose body mass placed massive gravitational loads on their skeleton. Previous studies investigated dinosaurian bone strength and biomechanics, but the relationships between dinosaurian trabecular bone architecture and mechanical behavior has not been studied. In this study, trabecular bone samples from the distal femur and proximal tibia of dinosaurs ranging in body mass from 23-8,000 kg were investigated. The trabecular architecture was quantified from micro-computed tomography scans and allometric scaling relationships were used to determine how the trabecular bone architectural indices changed with body mass. Trabecular bone mechanical behavior was investigated by finite element modeling. It was found that dinosaurian trabecular bone volume fraction is positively correlated with body mass like what is observed for extant mammalian species, while trabecular spacing, number, and connectivity density in dinosaurs is negatively correlated with body mass, exhibiting opposite behavior from extant mammals. Furthermore, it was found that trabecular bone apparent modulus is positively correlated with body mass in dinosaurian species, while no correlation was observed for mammalian species. Additionally, trabecular bone tensile and compressive principal strains were not correlated with body mass in mammalian or dinosaurian species. Trabecular bone apparent modulus was positively correlated with trabecular spacing in mammals and positively correlated with connectivity density in dinosaurs, but these differential architectural effects on trabecular bone apparent modulus limit average trabecular bone tissue strains to below 3,000 microstrain for estimated high levels of physiological loading in both mammals and dinosaurs. Rocky Mountain bighorn sheep rams (Ovis canadensis canadensis) routinely conduct intraspecific combat where high energy cranial impacts are experienced. Previous studies have estimated cranial impact forces up to 3,400 N and yet the rams observationally experience no long-term damage. Prior finite element studies of bighorn sheep ramming have shown that the horn reduces brain cavity translational accelerations and the bony horncore stores 3x more strain energy than the horn during impact. These previous findings have yet to be applied to applications where impact force reduction is needed, such as helmets and athletic footwear. In this study, the velar architecture was mimicked and tested to determine suitability as novel material architecture for running shoe midsoles. It was found that velar bone mimics reduce impact force (p < 0.001) and higher energy storage during impact (p < 0.001) and compression (p < 0.001) as compared to traditional midsole architectures. Furthermore, a quadratic relationship (p < 0.001) was discovered between impact force and stiffness in the velar bone mimics. These findings have implications for the design of novel material architectures with optimal stiffness for minimizing impact force.
Open Access
Dynamic structural analysis of ramming in bighorn sheep
(Colorado State University. Libraries, 2015) Drake, Aaron Michael, author; Haut Donahue, Tammy L., advisor; Donahue, Seth W., advisor; Stansloski, Mitchell, committee member; Heyliger, Paul, committee member
Concussions are the most common traumatic brain injury and are caused by impulsive loads applied to the skull, resulting in relative motion of the brain within the brain cavity. Despite wearing helmets, athletes involved in full contact sports, such as football, are highly susceptible to concussive injuries. Short term symptoms of concussions include nausea, headache and confusion and there is evidence of more serious, long term effects from repeated concussions. Furthermore, the physical mechanisms of concussions are not well understood, making them difficult to diagnose and treat clinically. Male bighorn sheep sustain massive impact loads to the head during ramming, which is done as a means of determining hierarchy and gaining mating privileges. These large animals thrust themselves, horns first, at one another and collide violently, repeating this ritual for up to several hours until the subdominant male succumbs. After a collision, the animals are stunned momentarily but otherwise appear to suffer no ill effects, based on behavioral observations. This simple fact provided the motivation to examine the dynamic structural behavior of bighorn sheep horns and skulls. For reference, the average translational brain cavity accelerations observed during finite element model impact were found to be 111g (1091 m/s²) and impacts thought to be damaging to human brains occur at around 100g. A dynamic finite element impact model was produced using the geometry, obtained from a CT scan, of a mature male bighorn sheep’s skull and horns. Quantitative and qualitative results of the simulation were examined to determine mechanisms of energy dissipation and stress distribution during an idealized impact event. Video analysis of particularly forceful ramming sequences of wild bighorn sheep was carried out to estimate the dynamics involved with ramming. In order to investigate the relative contributions of the horn curl as well as the internal foamy bone architecture, three separate finite element models were produced. One model had one half of the horn length removed, another had the internal foam-like bone removed and these models were compared to the fully intact model to determine the structural contributions of these features during impact. Removing one half of the horn curl had the effect of increasing the peak brain cavity translational acceleration by 49%. Eliminating the internal foamy bone architecture resulted in a dramatic 442% increase in brain cavity rotational accelerations. The dynamic (vibrational) response of bighorn sheep horns and skulls was investigated using two, related methods: finite element modal analysis and experimental modal analysis. The finite element modal analysis revealed five dominant natural frequencies with values ranging from 118 to 309 Hz. Experimental modal analysis revealed several natural frequencies between 100 and 300 Hz, however, differentiating specific modes was difficult. For both vibrational analyses the dominant vibrational mode shape was side-to-side oscillations of the horn tip. This study hopes to promote and guide further research on the mechanisms of brain trauma prevention in bighorn sheep, with an emphasis on the structural and material characteristics of the horn and skull, to increase our understanding of, and ways to prevent traumatic brain injuries in humans.